1. Field of the Invention
The present invention relates to a wireless audio system, and more particularly, to an interference-resistant wireless audio system and related method.
2. Description of the Prior Art
In recent years, due to the progressive development of wireless communications technology, a variety of electronic device comprising a wireless communication module can wirelessly transmit and receive audio signals and data signals.
Please refer to FIG. 1, which is a functional block diagram of a wireless audio system 10 according to the prior art. The wireless audio system 10 comprises a transmitter 12 for transforming an analog audio signal into an RF signal and for transmitting the RF signal into the air, and a receiver 14 for receiving the RF signal in the air and for transforming the received RF signal into a corresponding analog audio signal. Therefore, a user can hear the analog audio signal from the receiver 14.
The transmitter 12 comprises an audio signal receiver 16, an audio data format converter 18, a frame & coding unit 20, a modulation module 22, and an RF transmitter 24.
The audio signal receiver 16, along with the audio data format converter 18, sample the analog audio signals and a plurality of digitized sampling data points are acquired, each of which corresponds to an amplitude and phase of the analog audio signal at a predetermined sampling rate. Then the sampling data points are transformed into a digital signal P1 formatted for the pulse-code modulation (PCM). Thereafter, the frame & coding unit 20 appends a header and a tail serving as an error protection code to the digital signal P1, and generates a bit-streamed frame signal P2, which will be transmitted to the modulation module 22 bit by bit. The modulation module 22 modulates the bit-streamed frame signal P2 into an analog base-band signal P3 suit for wireless communications. Subsequently, the RF transmitter 24 up-converts the analog base-band signal P3 into an RF signal P4, and wirelessly transmits the RF signal P4 into the air.
The receiver 14 comprises an RF receiver 26, a demodulation module 28, a frame synchronization controller 30, a digital-to analog converter (DAC) 32, and a detachable speaker 34.
After receiving the RF signal P4 transmitted by the transmitter 12, the RF receiver 26 down-converts the RF signal P4 into a base-band signal P5, which corresponds to the base-band signal P3. The demodulation module 28 then demodulates the base-band signal P5 into a bit-streamed frame signal P6 corresponding to the frame signal P2 which is suit for digitally serial transmission. The frame synchronization controller 30 parses the header and the tail appended to the frame signal P6, and identifies the correctness to acquire a digital audio signal P7. After the DAC 32 transforms the digital audio signal P7 into an analog audio signal, the speaker 34 plays the analog audio signal transformed by the DAC 32.
Ideally, the analog audio signal played by the speaker 34 should be the same as that inputted into the audio signal receiver 16. Besides, all wireless communication devices usually use the unlicensed band, such as 2.4 G ISM band or 5 G ISM band, which are defined by the wireless legislation of Governments. For example, FCC in US or CE in Europe.
Please refer to FIG. 7 and FIG. 2. FIG. 7 lists a plurality of channels and their corresponding channel center frequencies in WLAN 802.11b and 802.11g standard. FIG. 2 is a frequency spectrum of the channels in WLAN 802.11b and 802.11g standard. As FIG. 2 shows, each of the channels occupies a bandwidth as wide as 22 MHz, while the difference between any two neighboring channel is as narrow as 5 MHz only. Thus, two RF signals respectively transmitted by the wireless communication devices will interfere with each other if the interval of the channels are not wider than four channels.
When a channel used by a wireless communication device is overlapped by another one, the RF signals transmitted by the wireless communication device are interferenced. Therefore, the severely distorted analog audio signals are generated, and the speaker 34 will mute in order not to output unendurable noises. Sometimes, the interference problem is so severe that a wireless communications link between the transmitter 12 and the receiver 14 is severely impacted or even failed.
When the distortion, the noises, or the fail of the wireless communication link resulted from the interference problem occur, the wireless audio system 10 executes the mute process to control the speaker 34 not to play the probably contaminated analog audio signal until the interference problem is gone. However, if the speaker 34 is playing music, the mute process will interrupt the music and spoils the mood of a user to enjoy the music.
In addition to the mute process, the wireless audio system 10 can get rid of the interference problem by switching the interferenced channel manually. However, the switching process is inconvenienced for the user because he has to switch the channel manually as hearing the noise.